The performance requirements for insulating materials exemplified by buffer coat materials and rewiring layer materials of LSI chips are becoming increasingly severe with respect to the properties of, for example, higher resolution, low-temperature heat treatment, low stress and low dielectric constant accompanying higher performance levels of LSI. In particular, in order to satisfy requirements for lower dielectric constants of interlayer insulating film materials, stress resistance and heat resistance have decreased, and in response to requirements for higher speeds placed on rewiring Cu layers, the Cu used for rewiring has tended to become thicker due to increased current density. Consequently, in addition to requirements for high resolution, chemical resistance and temperature stress resistance, buffer coat materials and rewiring layer materials are also being required to satisfy requirements with respect to thick film formation ability, flatness, low stress, low dielectric constant and low-temperature heat curing treatment.
In the past, photosensitive polyimides, for example, were used as a typical example of an LSI chip buffer coat material. Compositions containing a polyimide precursor, having a photopolymerizable double bond in a side chain thereof, and a photopolymerization initiator were widely used as photosensitive polyimides. These compositions were spin-coated onto an LSI wafer followed by crosslinking the double bonds of the side chain in a photo-crosslinking reaction by irradiating with light through a photomask. Subsequently, a pattern was formed during development and simultaneous to decomposing and volatizing the crosslinked chains by heat curing treatment, a patterned insulating film was formed by forming a polyimide structure. An insulating film composed of a polyimide formed in this manner has superior heat resistance, chemical resistance and mechanical properties.
Problems associated with these photosensitive polyimides include susceptibility to crack formation when forming a thick film due to the large residual stress, low flatness with respect to level differences in the surface of the LSI wafer caused by shrinkage of nearly 40% during heat curing treatment, and inferior mechanical properties due to inadequate formation of the polyimide structure at low heat curing treatment temperatures of 200° C. or lower.
In contrast, a photosensitive silicone compound known as Ormocer One manufactured by Fraunhofer ISC of Germany is disclosed in Patent Document 1 that is obtained by condensing a trialkoxysilane having a photopolymerizable functional group and a diaryl silanediol. A composition of this compound and a photopolymerization initiator enables the formation of a negative pattern by irradiating with light, the pattern can be heat-cured at a low temperature of 150° C., and the insulating film after curing has heat resistance equivalent to that of polyimides on the order of 300° C. or higher. On the other hand, as is exemplified by properties such as low residual stress of 10 MPa or less, the absence of shrinkage caused by heat curing treatment, and film thickness loss of within 3% before and after heat curing, it has superior properties that cannot be achieved with polyimides.
Patent Document 1 discloses (meth)acryloxy groups and styryl groups as examples of photopolymerizable functional groups possessed by the photosensitive silicone compound.
In addition, Patent Document 2 discloses a photopolymerizable or thermal polymerizable silicone resin in the form of a photosensitive silicone compound obtained by reacting vinyl phenyl methyl diethoxysilane having a styryl group and diisobutyl silanediol.    Patent Document 1: Canadian Patent No. 2378756    Patent Document 2: US Patent Application No. 2004/0242830